Yes, if you have your connection pool set to 30 connections then it will make 30 connections * the number of data nodes. However, that many connections are rarely needed. The connections are multiplexed, allowing multiple simultaneous requests per connection, so you should probably have a smaller pool.
You could also look at moving to SDK 3.1.1. This version of the SDK introduced some changes to connection buffers, they now use System.IO.Pipelines. This allows it to use a reusable pool of chunked buffers from the ArrayPool. This should reduce the memory pressure you experience, except under high load with large documents.